A liquid crystal display device is used as the display device of high resolution color monitors of computers and other information equipments, or television receivers. A liquid crystal display device fundamentally includes a liquid crystal display portion in which liquid crystals are sandwiched between two substrates of which at least one is made of transparent glass or the like. In addition, a liquid crystal display device includes a driver for selectively applying voltages to pixel electrodes formed on the substrate of the liquid crystal display portion. Pixels of the respective pixel electrodes are controlled based on the voltage application by the driver.
A liquid crystal display portion generally includes gate signal lines, source signal lines and pixel electrodes. The gate signal lines, for instance, respectively extend in the horizontal direction (main scanning direction), and are aligned in the vertical direction (sub scanning direction). The source signal lines, for instance, respectively extend in the vertical direction (sub scanning direction), and are aligned in the horizontal direction (main scanning direction). Thin film transistors (TFT) and pixel electrodes are disposed in a matrix at the intersection points of the gate signal lines and the source signal lines. The driver applies voltages to the gate signal lines for turning the TFT ON and OFF. Moreover, the driver applies voltages based on the input image signal to the pixel electrodes via the source signal lines, to thereby change transmittance of the liquid crystals provided corresponding to the pixel electrodes to a value according to the applied voltage. Here, the driver retains the input image signal for one horizontal period, and outputs the input image signal to the source signal lines of the liquid crystal display portion.
In general, when DC drive voltages are applied to the pixel electrodes for driving the liquid crystals, the liquid crystals become deteriorated and the life thereof is shortened, and hence, an AC voltage drive of inverting the polarity of the voltage applied to the pixel electrodes for each frame is performed in a liquid crystal display portion. As the drive modes of the liquid crystal display portion for performing the AC voltage drive, a column inversion drive mode and a dot inversion drive mode are known. The column inversion drive mode is a drive mode of applying voltages of the same polarity to the pixel electrodes connected to the same source signal line, inverting the polarity of the voltage applied to the pixel electrodes connected to mutually adjacent source signal lines in the respective frames, and inverting the polarity of the voltage applied to the respective pixel electrodes for each frame. The dot inversion drive mode is a drive mode of applying voltages of a reverse polarity to mutually adjacent pixel electrodes in the respective frames, and inverting the polarity of the voltage applied to the respective pixel electrodes for each frame.
Here, the column inversion drive mode and the dot inversion drive mode are compared. In the column inversion drive mode, polarities of voltages applied to the pixel electrodes connected to the source signal line are the same throughout one frame period. Thus, the column inversion drive mode is a drive mode that is advantageous in the data writing (voltage application) to the pixel electrodes, and is suitable when a long data writing time may not be secured. Meanwhile, the column inversion drive mode is inferior in terms of performance against crosstalk and flicker. Contrarily, although the dot inversion drive mode causes superior performance against crosstalk and flicker, it takes a relatively long period of time to write data to the pixel electrodes.
Thus, the device described in JP-A-2005-215591 switches the drive mode of the liquid crystal display portion to be the column inversion drive mode when the frame rate of the input image signal is high, and to be the dot inversion drive mode when the frame rate of the input image signal is low.
Switching the drive mode of the liquid crystal display portion directly between the dot inversion drive mode and the column inversion drive mode is likely to cause a drastic load change and discontinuous image display on the liquid crystal display portion during the switching of the drive mode, which results in a boundary between images. In the foregoing case, image display quality may deteriorate. However, the device described in foregoing JP-A-2005-215591 fails to give any consideration to this point.